docs: def fromMessage(cls, message):
          """Generate a ServerError instance, extracting the error text
          and the error code from the message."""
          error_text = message.getArg(
              OPENID_NS, 'error', '<no error message supplied>')
          error_code = message.getArg(OPENID_NS, 'error_code')
          return cls(error_text, error_code, message)